My Corydoras Behaviour

I have 5 Corydoras I am trying to find out about some rather odd habits mine have. This is swimming at high speed back and forth across the tank almost continuously!!! I thought they were supposed to be bottom feeders. Although they do this, its true, but most of the time is spent speeding across the tank. It seems quite bizarre, Is there anyone out there that has Cordys or knows if this is normal behaviour? if so can you enlighten me or perhaps let me know if they could be suffering from something? I am feeding them various frozen foods that come in push out pouches plus Algae wafers and occasionally the dry flakes. They are voracious eaters when they are still long enough!!! Thank you